Buckling mode actuation of fiber scanner to increase field of view

ABSTRACT

Described herein are embodiments of fiber scanning systems and methods of scanning optical fibers. The disclosed systems and methods advantageously provide an improvement to the scanning range, the oscillation amplitude, and/or the maximum pointing angle for an optical fiber in a fiber scanning system by inducing a buckling of a portion of the optical fiber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. ProvisionalApplication No. 62/481,497, filed on Apr. 4, 2017, which is herebyincorporated by reference in its entirety.

BACKGROUND

Scanning devices typically trade off scanning range for frequency. Ingeneral, as frequency is increased, scanning range decreases, and asfrequency decreases, scanning range can be increased. In someapplications, however, it is desirable to increase both frequency andscanning range. Additional scanning system designs are needed to improveand expand the scanning range and utility of scanning systems.

SUMMARY

This application relates to optical fiber scanner systems and relatedmethods. More specifically, and without limitation, this applicationrelates to optical fiber oscillators, such as used for scanning fiberdisplays, where the optical fibers are oscillated in a whirling motionby way of a mechanical actuator, such as a piezoelectric actuator(piezo). The optical fibers are further induced to buckle by applicationof a compressive force, where the buckling increases a maximumdeflection of the optical fiber, which may increase the field of view ofthe system. The combination of buckling and whirling, in embodiments,can provide a useful increase in field of view, as compared to whirlingonly systems, without sacrificing size, form factor, or frequency.

In optical scanning systems, frequency may be important for bothresolution and refresh rate, and two distinct frequency regimes may beuseful to consider. For example, in a scanning fiber display, a firstfrequency may be related to the refresh rate, where repeated scans of afiber may dictate how frequently the output view can be changed. Asecond frequency regime may be related to the individual oscillationswithin a single scan, and this frequency may impact the resolution bydictating how fine the distinctions between non-overlapping motions ofthe fiber can be and how quickly these motions can be made within asingle scan of the fiber.

Range, however, may be important for field-of-view for a given projectordesign. For example, the maximum amplitude or range of an oscillatingfiber may provide for a limit on how wide an output image generated bythe fiber may be. As the oscillation range is increased, a wider fieldof view may be provided.

Scanning devices may be useful as display devices due to their smallform factor and useful resolution and field-of-view. However, in orderto obtain high frequency scanning devices with a high scanning range,innovations in this field are required. The presently described opticalfiber scanning systems allow for improved field-of-view projectors whilemaintaining a small form factor. As an example, by incorporating thedisclosed scanning systems into a scanning fiber display projector, thefield-of-view of the projector may be increased relative to conventionalscanning fiber display devices.

Without limitation, the present application provides devices andsystems, such as optical fiber scanning devices or systems that comprisean optical fiber. In an aspect, an optical fiber scanning systemcomprises an optical fiber having a distal fiber end and a proximalfiber end; a first electromechanical transducer mechanically coupled tothe optical fiber between the distal fiber end and the proximal fiberend, such as a first electromechanical transducer that is configured toapply a buckling force to the optical fiber; and a secondelectromechanical transducer mechanically coupled to the optical fiberbetween the distal fiber end and the proximal fiber end, such as asecond electromechanical transducer that is configured to excitewhirling of the distal fiber end. In embodiments, the distal fiber endis unconstrained, which may allow the distal fiber end to deflectlaterally in response to mechanical actuation.

Optionally, a first joint mechanically coupling the firstelectromechanical transducer and the optical fiber has a first axialstiffness along an axis parallel to a longitudinal axis of the opticalfiber. Optionally, a second joint mechanically coupling the secondelectromechanical transducer and the optical fiber has a second axialstiffness along the axis parallel to the longitudinal axis of theoptical fiber. In embodiments, the first axial stiffness and the secondaxial stiffness are sufficient to induce buckling of the optical fiberwhen a distance between the first joint and the second joint is reducedby a particular distance, such as a minimum distance less than 5 μm, bya distance of between 1 μm and 5 μm, or by greater distances, such asbetween 1 μm and 50 μm, between 5 μm and 10 μm, between 10 μm and 20 μm,between 20 μm and 30 μm, between 40 μm and 50 μm, or more than 50 μm.

Various configurations for the first electromechanical transducer andthe second electromechanical transducers are useful with the opticalfiber scanning systems described herein. For example, the firstelectromechanical transducer optionally corresponds to a buckling piezohaving a distal buckling end and a proximal buckling end. The opticalfiber may be mechanically coupled to the distal buckling end, theproximal buckling end, or both the distal buckling end and the proximalbuckling end. In embodiments, the buckling piezo is a piezo tube orpiezo stack. Optionally, the optical fiber passes through the piezo tubeor the piezo stack. The buckling piezo may include a plurality ofelectrodes for controlling a length of the buckling piezo by applicationof one or more voltages. For example, reducing a length of the bucklingpiezo between the distal buckling end and the proximal buckling endapplies the buckling force to the optical fiber.

In another example, the second electromechanical transducer correspondsto a piezo tube, such as a whirling piezo tube, having a distal tube endand a proximal tube end. In embodiments, the optical fiber passesthrough the whirling piezo tube. The distal tube end may be mechanicallycoupled to the optical fiber by a whirling distal joint. Optionally, theoptical fiber is mechanically coupled to the distal tube end, theproximal tube end, or both the distal tube end and the proximal tubeend, depending on the particular configuration used in the opticalscanning system. Optionally, the distal fiber end extends beyond thedistal tube end, and the distal tube end is positioned between thedistal fiber end and the proximal tube end. In embodiments, the proximalfiber end extends beyond the proximal tube end and the proximal tube endis positioned between the proximal fiber end and the distal tube end.Optionally, the optical fiber is not fixed to the proximal tube end.

In embodiments, the whirling piezo tube includes a plurality ofelectrodes for controlling lateral deflections of a distal tube end ofthe piezo tube by application of one or more voltages, such as to inducewhirling of the distal end of the optical fiber. In embodiments, thewhirling piezo tube has an inner diameter sufficient to accommodatebuckling of the optical fiber. The whirling distal joint may have anaxial stiffness along a longitudinal axis of the whirling piezo tube,such as an axial stiffness that is sufficient to induce buckling of theoptical fiber. The he whirling distal joint may have a lateral stiffnessthat is sufficient to accommodate lateral rotation of the optical fiberduring buckling.

In some embodiments, the optical fiber scanning system further comprisesa support tube mechanically coupled to the whirling piezo tube and thefirst electromechanical transducer. Optionally the firstelectromechanical transducer is positioned inside the support tube.Optionally, the first electromechanical transducer corresponds to abuckling piezo tube, as described above, such as a buckling piezo tubehaving a distal buckling end and a proximal buckling end. Inembodiments, the distal buckling end is positioned between the proximaltube end and the proximal buckling end. In some embodiments, the opticalfiber and the distal buckling end are mechanically coupled by a bucklingdistal joint, and movement of the buckling distal joint along alongitudinal fiber axis causes buckling of the optical fiber between thebuckling distal joint and the whirling distal joint. Optionally, thesupport tube has a distal end and a proximal end, such as a distal endof the that is mechanically coupled to the proximal tube end by awhirling proximal joint, and a proximal end that is mechanically coupledto the proximal buckling end by a buckling proximal joint.

In another example, the second electromechanical transducer includes ahub, a frame surrounding the hub, and a plurality of lateralelectromechanical transducers mechanically coupled to the frame and tothe hub. In some embodiments, the optical fiber passes through the huband the hub is mechanically coupled to the optical fiber by a whirlingjoint. The second electromechanical transducer optionally includes aplurality of flexures extending radially from the hub and coupling thehub to the frame. The lateral electromechanical transducers maycorrespond to piezo elements including electrodes for controllinglateral deflections of the hub to excite whirling of the distal fiberend. For example, application of one or more voltages to the electrodesmodifies a controls a length of the piezo elements. Optionally, thepiezo elements may be actuated in sequence to move the whirling joint ina laterally rotating motion.

In another example, the first and second electromechanical transducersmay be combined. For example, the first electromechanical transducer andthe second electromechanical transducer may optionally comprise a piezotube, such as a piezo tube that has a distal tube end and a proximaltube end. Optionally, the optical fiber passes through the piezo tubeand the distal fiber end extends beyond the distal tube end. The distaltube end and the optical fiber may be mechanically coupled at a distaljoint. The proximal tube end and the optical fiber may be mechanicallycoupled at a proximal joint. In some embodiments, the distal joint andthe proximal joint have axial stiffnesses along a longitudinal axis ofthe piezo tube that are sufficient to induce buckling of the opticalfiber, such as when a length of the piezo tube is reduced. Optionally,the distal joint has a lateral stiffness that is sufficient toaccommodate lateral rotation of the optical fiber during buckling. Inembodiments, the piezo tube has an inner diameter sufficient toaccommodate buckling of the optical fiber between the distal joint andthe proximal joint. In embodiments, the distal tube end is positionedbetween the distal fiber end and the proximal tube end, the proximalfiber end extends beyond the proximal tube end, and the proximal tubeend is positioned between the proximal fiber end and the distal tubeend.

In embodiments, the piezo tube includes a plurality of electrodes forcontrolling lateral deflections of a distal tube end of the piezo tubeend and for controlling a length of the piezo tube, such as byapplication of one or more voltages. Optionally, voltages may besuperimposed on one another to induce simultaneous buckling andwhirling. For example, a buckling voltage may be simultaneously appliedto each of the plurality of electrodes to cause a length of the piezotube along a longitudinal tube axis to change, and different whirlingvoltages applied individually to the plurality of electrodes to causethe distal tube end to deflect laterally, such as in a spiralconfiguration.

In a specific embodiment, an optical fiber scanning system comprises afirst electromechanical transducer mechanically coupled to the opticalfiber, such as a first electromechanical transducer that is configuredto apply a buckling force to the optical fiber; and a secondelectromechanical transducer mechanically coupled to the optical fiber,such as a second electromechanical transducer that configured to excitewhirling of the optical fiber.

It will be appreciated that the whirling and buckling motions maycombine to increase a field of view of an optical fiber scanner beyondthat available from a whirling-only fiber scanner. Optionally, thebuckling force periodically ramps in amplitude. Optionally, a whirlingamplitude of the fiber periodically ramps. Optionally, ramping of thebuckling force and ramping of the whirling amplitude are synchronized.Optionally, piezos may be used as the electromechanical transducers, asdescribed above.

For example, an optical fiber scanning system may comprise a piezo tube;an optical fiber passing through the piezo tube; a support tubemechanically coupled to the piezo tube; and a buckling piezo disposedinside the support tube and mechanically coupled to the optical fiber.It will be appreciated that the optical fiber may also pass through aninterior space defined by the buckling piezo.

It will be appreciated that a variety of piezo tubes are useful with thedisclosed optical fiber scanning systems and devices and methods. Forexample, a piezo tube may optionally comprise a radially poledpiezoelectric tube. Optionally, a piezo tube may comprise a piezo stack.A piezo tube may have an inner diameter of a dimension sufficient toaccommodate buckling of the optical fiber, such as an inner diameterthat is greater than an outer diameter of the optical fiber. Suchdifferences in diameters may allow the optical fiber to buckle inside ofthe piezo tube without contacting an inner surface of the piezo tube.

In various embodiments, the piezo tube has a distal tube end and aproximal tube end. It will be appreciated that the terms distal andproximal are relative terms referencing different positions or ends of acomponent. For example, the optical fiber has a distal fiber end and aproximal fiber end. The distal fiber end of the optical fiber may extenddistally beyond a distal tube end of the piezo tube. For example, thedistal tube end of the piezo tube may be positioned between the distalfiber end of the optical fiber and a proximal tube end of the piezotube. The proximal fiber end of the optical fiber may extend proximallybeyond a proximal tube end of the piezo tube. For example, the proximaltube end of the piezo tube may be positioned between the proximal fiberend of the optical fiber and the distal tube end of the piezo tube. Inembodiments, the distal fiber end of the optical fiber is unconstrained.Optionally, the optical fiber is not fixed to the proximal tube end.

Various optical fibers are useful with the disclosed optical fiberscanning systems and devices and methods. For example, the optical fiberoptionally comprises one or more of a cladding, one or more cores, asingle-mode optical fiber, a multi-mode optical fiber, a step-indexoptical fiber, a photonic crystal optical fiber, a visible opticalwaveguide, an infrared optical waveguide, an ultraviolet opticalwaveguide, and a plurality of optical fibers.

In order to achieve buckling of the optical fiber, various componentsmay be mechanically coupled to one another. For example, the opticalfiber and a distal tube end of the piezo tube may be mechanicallycoupled by a whirling distal joint. As used herein, “whirling distaljoint” and “distal whirling joint” may be used interchangeably. It willbe appreciated that the whirling distal joint may have an axialstiffness along the tube axis that is sufficient to induce buckling ofthe optical fiber. Optionally, the whirling distal joint has a lateralstiffness that is sufficient to accommodate lateral rotation of theoptical fiber during buckling. In some embodiments, the whirling distaljoint has an axial stiffness along the tube axis that is sufficient toinduce buckling of the optical fiber when a distance between thewhirling distal joint and a buckling distal joint is reduced by athreshold amount or more, such as a threshold amount less than about 5μm, such as between about 0.01 μm and about 5 μm or between about 0.1 μmand about 5 μm.

Additionally or alternatively, the buckling distal joint mechanicallycouples the optical fiber and the buckling piezo. As used herein,“buckling distal joint” and “distal buckling joint” may be usedinterchangeably. In embodiments, the buckling piezo has a distal piezoend and a proximal piezo end. For example, the distal piezo end of thebuckling piezo is positioned between a proximal tube end of the piezotube and the proximal piezo end of the buckling piezo. Optionally, theoptical fiber and the distal piezo end of the buckling piezo aremechanically coupled by a buckling distal joint. For example, movementof the buckling distal joint along a fiber axis may cause buckling ofthe optical fiber between the buckling distal joint and a whirlingdistal joint.

Various configurations are contemplated for the buckling piezos usedwith the systems, devices and methods described herein. For example, thebuckling piezo optionally comprises a second piezo tube. Optionally, thebuckling piezo comprises a piezo stack.

To achieve whirling motion, application of voltages to a piezo tube maybe used to change a dimensional characteristic of the piezo tube. Forexample, the piezo tube may include a plurality of electrodes, such asfor controlling lateral deflections of a distal tube end of the piezotube by application of one or more voltages. Optionally, the pluralityof electrodes includes a first pair of electrodes extending along alength of the piezo tube and arranged 180° from one another. Optionally,the plurality of electrodes includes a second pair electrodes extendingalong the length of the piezo tube and arranged 180° from one anotherand 90° from the first pair of electrodes. Optionally, an inner surfaceof the piezo tube provides a voltage ground for the plurality ofelectrodes.

To achieve buckling motion, application of voltages to a buckling piezomay be used to change a dimensional characteristic of the bucklingpiezo. For example, the buckling piezo may include a plurality ofelectrodes, such as for controlling a length of the buckling piezo byapplication of one or more voltages.

Application of voltages to a piezo element may be achieved by use of oneor more voltage sources. For example, an optical fiber scanning systemmay further comprise a voltage source in electrical communication withthe plurality of electrodes of a piezo tube, such as a voltage sourcethat applies one or more whirling voltages to the plurality ofelectrodes. Example whirling voltages have a frequency of between about10 kHz and about 80 kHz. Alternatively or additionally, an optical fiberscanning system may further comprise a voltage source in electricalcommunication with the plurality of electrodes of a buckling piezo, suchas a voltage source that applies a buckling voltage to the plurality ofelectrodes. Example buckling voltage may have a frequency or repetitionrate of between about 15 Hz and about 300 Hz.

In embodiments including a support tube, the support tube may have adistal end and a proximal end. For example, the distal end of thesupport tube and a proximal tube end of the piezo tube may bemechanically coupled by a whirling proximal joint. As used herein,“whirling proximal joint” and “proximal whirling joint” may be usedinterchangeably. The proximal end of the support tube and a proximalpiezo end of the buckling piezo may be mechanically coupled by abuckling proximal joint. As used herein, “buckling proximal joint” and“proximal buckling joint” may be used interchangeably.

Different optical fiber scanning system configurations are contemplated,which may include one or more of the features described above. Forexample, an optical fiber scanning system may comprise a piezo tube,such as a piezo tube that has a tube axis, one or more lateral axes, adistal tube end, and a proximal tube end; an optical fiber passingthrough the piezo tube; a distal joint mechanically coupling the distaltube end of the piezo tube and the optical fiber, such as a distal jointthat has an axial stiffness along the tube axis that is sufficient toinduce buckling of the optical fiber; and a proximal joint mechanicallycoupling the proximal tube end of the piezo tube and the optical fiber.Optionally, the distal joint may have a lateral stiffness that issufficient to accommodate lateral rotation of the optical fiber duringbuckling. Optionally, the distal joint has an axial stiffness along thetube axis that is sufficient to induce buckling of the optical fiberwhen a distance between the distal joint and the proximal joint isreduced by at least a threshold amount, such as a threshold amount thatis about 5 μm or less, such as between 0.01 μm and 5 μm, between 0.1 μmand about 5 μm, or between 1 μm and 5 μm. It will be appreciated thatuseful piezo tubes include those having an inner diameter sufficient toaccommodate buckling of the optical fiber between the distal joint andthe proximal joint.

In embodiments, the optical fiber has a distal fiber end and a proximalfiber end, such as a distal fiber end of the optical fiber that extendsdistally beyond the distal tube end of the piezo tube. Optionally, thedistal tube end of the piezo tube is positioned between the distal fiberend of the optical fiber and the proximal tube end of the piezo tube.Optionally, the proximal fiber end of the optical fiber extendsproximally beyond the proximal tube end of the piezo tube. Optionally,the proximal tube end of the piezo tube is positioned between theproximal fiber end of the optical fiber and the distal tube end of thepiezo tube. It will be appreciated that the distal fiber end of theoptical fiber may be unconstrained. In embodiments, the proximal fiberend extends proximally beyond the proximal tube end of the piezo tube,and the distal fiber end extends distally beyond the distal tube end ofthe piezo tube.

A piezo tube may include a plurality of electrodes, such as forcontrolling lateral deflections of a distal tube end of the piezo tubeend and a length of the piezo tube by application of one or morevoltages. For example, the plurality of electrodes includes a first pairof electrodes extending along a length of the piezo tube and arranged180° from one another. Optionally, the plurality of electrodes includesa second pair electrodes extending along the length of the piezo tubeand arranged 180° from one another and 90° from the first pair ofelectrodes. Optionally, a buckling voltage is applied to the pluralityof electrodes causes a length of the piezo tube to change, such assimultaneously with a whirling voltage.

It will be appreciated that a voltage source may be included inelectrical contact with a plurality of electrodes. The voltage sourcemay apply one or more whirling voltages to the plurality of electrodes,such as one or more whirling voltages that have a frequency of betweenabout 10 kHz and about 80 kHz. Optionally, the voltage source appliesone or more whirling voltages to the plurality of electrodes, such asone or more whirling voltages that have a frequency about equal to anatural frequency of a cantilevered portion of the optical fibercorresponding to a region of the optical fiber between the distal jointand a distal fiber end of the optical fiber. Optionally, voltage sourcemay alternatively or additionally apply a buckling voltage to theplurality of electrodes, such as a buckling voltage that has a frequencyof between about 15 Hz and about 300 Hz, such as about 60 Hz or about120 Hz.

In another aspect, methods of scanning an optical fiber are provided.For example, a method of this aspect comprises applying a first voltageto an optical fiber scanning system to induce whirling of an opticalfiber, applying a second voltage to the optical fiber scanning system toinduce buckling of the optical fiber. The optical fiber scanning systemused for methods of this aspect may correspond to any of the opticalfiber scanning systems described herein, such as an optical fiberscanning system including the optical fiber, a first electromechanicaltransducer mechanically coupled to the optical fiber between the distalfiber end and the proximal fiber end and configured to apply a bucklingforce to the optical fiber; and a second electromechanical transducermechanically coupled to the optical fiber between the distal fiber endand the proximal fiber end and configured to excite whirling of thedistal fiber end. Optionally, the first electromechanical transducerincludes a plurality of electrodes, and applying the second voltageincludes applying the second voltage to the plurality of electrodes toinduce longitudinal application of the buckling force. Optionally, thesecond electromechanical transducer includes a plurality of electrodes,and applying the first voltage includes applying the first voltage tothe plurality of electrodes to induce lateral deflection of the opticalfiber for exciting whirling of the distal fiber end. In someembodiments, whirling of the optical fiber causes the distal fiber endto deflect a first predetermined amount. In some embodiments, bucklingof the optical fiber causes deflection of the distal fiber end by asecond predetermined amount that is superimposed on the firstpredetermined amount.

In a specific embodiment, a method of scanning an optical fiber maycomprise applying a first voltage to an optical fiber scanning system toinduce whirling of an optical fiber of the optical fiber scanningsystem, such as any of the optical fiber scanning systems describedherein. As an example, such an optical fiber scanning system may includea piezo tube, such as a piezo tube that includes a plurality ofelectrodes for controlling lateral deflections of a distal tube end ofthe piezo tube by application of the first voltage, and an optical fiberpassing through the piezo tube.

The first voltage optionally has a sinusoidal profile, such as asinusoidal profile that has a variable amplitude. Optionally, methods ofthis aspect comprise or further comprise applying a second voltage tothe optical fiber scanning system to induce buckling of the opticalfiber.

As another example, an optical fiber scanning system useful with themethods of this aspect may comprise or further comprise a buckling piezohaving a second plurality of electrodes. Optionally, applying the secondvoltage includes applying the second voltage to the second plurality ofelectrodes to induce axial expansion or contraction of the bucklingpiezo, such as along a length of the buckling piezo. Optionally,applying the second voltage includes applying the second voltage to theplurality of electrodes to induce axial expansion or contraction of thepiezo tube. Example second voltages include those having a frequency ofbetween about 15 Hz and about 300 Hz, such as about 60 Hz or about 120Hz. Example the second voltage may exhibit a sawtooth or triangularprofile. Optionally, a delay may be used before the second voltage isapplied. For example, applying the second voltage may include applyingthe second voltage a predetermined amount of time after applying thefirst voltage. It will be appreciated that applying the second voltagemay include applying the second voltage after whirling of the opticalfiber causes the optical fiber to deflect a predetermined amount.Optionally, whirling of the optical fiber causes the optical fiber todeflect a first predetermined amount and buckling of the optical fibercauses the optical fiber to deflect a second predetermined amountsuperimposed on the first predetermined amount. It will be appreciatedthat whirling of the optical fiber may corresponds to an end of theoptical fiber moving in a circular path, a spiral path, with a Lissajoumotion, etc.

The foregoing, together with other features and embodiments, will becomemore apparent upon referring to the following description, claims andaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a schematic illustrations of an example fiber scanningsystem showing increased fiber deflection with use of buckling of theoptical fiber.

FIG. 2A provides a schematic illustration of a piezo tube component of afiber scanning system and FIG. 2B provides a schematic overview ofwhirling motion of the piezo tube.

FIG. 3 provides a schematic illustration of a cross-section of anexample fiber scanning system of some embodiments.

FIG. 4 provides a plot of example voltages applied to differentelectrodes of a piezo tube of a fiber scanning system for inducing awhirling motion.

FIG. 5 provides a plot of example voltages applied to electrodes of apiezo of a fiber scanning system for inducing a buckling motion.

FIG. 6 provides a schematic illustration of a cross-section of anexample fiber scanning system of some embodiments.

FIG. 7 provides a schematic illustration of a cross-section of anexample fiber scanning system of some embodiments.

FIG. 8A, FIG. 8B, FIG. 8C, and FIG. 8D provide schematic illustrationsof an example fiber scanning system of some embodiments.

FIG. 9 provides optical images of a fiber scanning system embodiment.

DETAILED DESCRIPTION

Described herein are embodiments of fiber scanning systems and methodsof scanning optical fibers. The disclosed systems and methodsadvantageously provide an improvement to the scanning range, theoscillation amplitude, and/or the maximum pointing angle for an opticalfiber in a fiber scanning system by inducing a buckling of a portion ofthe optical fiber.

It will be appreciated that the term “buckling” refers to acharacteristic deformation that a structure will exhibit under acompressive load. Buckling may occur as the result of application of aforce to an end of a structure or between two points within thestructure. Buckling may result in a deformation of the structure that istransverse or otherwise not coaxial to the direction of the appliedforce. Buckling is commonly observed or characterized in columnar orelongated structures, where the structure will bow, flex, or bendbetween points of applied force, which may be applied at a fixed end ofthe structure, at a free end of the structure, or generally between twoarbitrary points of the structure. Depending on the magnitude,direction, and location of the force applied, how quickly the force isapplied, and the material properties of the structure, buckling can takeon different modes. It will be appreciated that characteristic shape ofthe buckling may be dependent upon boundary conditions of the buckledstructure, such as how and whether the ends of the structure are fixedor supported. The buckling employed in the present inventionsadvantageously make use of buckling modes in which a deflection of afree end of an optical fiber is amplified or otherwise increased bybuckling occurring between points along the fiber's axis.

FIG. 1 provides a schematic illustration of an example fiber scanningsystem 100. As illustrated, fiber scanning system 100 includes a piezotube 105 and an optical fiber 110 passing through piezo tube 105. Itwill be appreciated that the term “piezo” is used interchangeably withthe terms “piezoelectric material,” “piezoelectric transducer,”“piezoelectric actuator,” and “piezoelectric device” and refers to amaterial that exhibits a piezoelectric effect, such as the generation ofa voltage when the material is deformed or the deformation of thematerial when a voltage or an electrical field is applied to thematerial. It will be appreciated that a variety of piezoelectricmaterials are useful with the systems and methods described herein.Example piezoelectric materials include certain ceramic materials, suchas lead zirconate titanate (PZT), and certain crystalline materials,such as quartz. A piezo may be used, in various embodiments, as anactuator by controlled application of voltages to the piezoelectricmaterial to induce controlled expansion, contraction, or deformation ofthe piezo. A piezo may have voltages applied between various points onthe piezo to provide expansions, contractions, or deformations in anydesired configuration, and application of voltages in particularconfigurations may result in deflection or bending motions in suitablydesigned piezo systems. For example, in some embodiments, a piezo tubemay comprise a radially poled piezoelectric tube with, for example, fouror more individual electrodes. Piezos may take on any suitable shape fora particular application. In some embodiments, piezos are constructed astubular structures, such as a cylindrical structure having a centralcylindrical opening. In other embodiments, piezos are constructed ascylindrical or cuboid shapes. Piezos may incorporate one or moreelectrodes to simplify or otherwise enable application of voltages todesired points on the material.

Piezo tube 105 may have a distal end 155 and a proximal end 160. Forexample, the distal end of piezo tube 105 may be free, while theproximal end 160 of piezo tube 105 may be fixed to another object orstructure in order to restrict motion of the proximal end 160 of piezotube 105 relative to the other object or structure. As used herein theterms “distal” and “proximal” are intended to reflect relative locationsof objects, such as a piezo tube or an optical fiber. Other structuresor objects may also be identified as having distal and proximallocations. For example, an optical fiber may have a distal end and aproximal end. The terms distal end and proximal end may refer tophysical ends of an object or may refer to a location of an objectdefining a particular region. It will be appreciated that proximal anddistal may be referenced relative to a single body or structure. In someembodiments, the terms proximal and distal may be interchanged with theterms first and second, top and bottom (or bottom and top), left andright (or right and left), etc. In one embodiment, the term proximal maybe referenced to a mechanical ground while the term distal is referencedat a distance from the mechanical ground.

Piezo tube 105 includes an inner diameter that is larger than an outerdiameter of optical fiber 110 such that there is space between opticalfiber 110 and the inner surface of piezo tube 105. This configurationmay allow piezo tube 105 to accommodate buckling of optical fiber 110,such as in buckling zone 115. It will be appreciated that the differencebetween the outer diameter of optical fiber 110 and inner diameter ofpiezo tube 105 may have any suitable magnitude such that optical fiber110 does not contact the inner surface of piezo tube 105 duringbuckling. In some configurations, however, contact between optical fiber110 and the inner surface of piezo tube 105 may result in a complexbuckling motion.

Optical fiber 110 may take on any suitable configuration. For example,optical fiber 110 may comprise a glass-, polymer-, or plastic-basedoptical fiber. Optical fiber 110 may optionally include a core andcladding. Optical fiber 110 may optionally comprise a multi-core opticalfiber. Optical fiber 110 may comprise a single-mode or multi-modeoptical fiber. Optical fiber 110 may comprise a photonic crystal opticalfiber. Optical fiber may comprise a visible optical waveguide, aninfrared optical waveguide, and/or an ultraviolet optical waveguide.Optical fiber 110 may optionally comprise a plurality of optical fibers.

Points between ends of optical fiber 110 may be fixed to other objects.For example, as depicted in FIG. 1, optical fiber 110 and a distal end155 of piezo tube 105 may be mechanically coupled at whirling distaljoint 120. Optical fiber 110 may be fixed at a buckling distal joint125. This configuration may advantageously allow optical fiber 110 tobuckle in buckling zone 115. It will be appreciated that buckling ofoptical fiber 110 may be accomplished by any suitable relative motionbetween whirling distal joint 120 and buckling distal joint 125. Forexample, buckling may be induced by shortening the distance betweenwhirling distal joint 120 and buckling distal joint 125, such as bymoving buckling distal joint 125 along a direction towards whirlingdistal joint 120. Optionally, buckling of optical fiber 110 in bucklingzone may be accomplished by shortening a length of piezo tube 105 suchthat whirling distal joint moves towards buckling distal joint 125.

Whirling distal joint 120 may comprise any suitable material tomechanically couple optical fiber 110 to the distal end 155 of piezotube 105. Advantageously, whirling distal joint 120 may exhibit an axialstiffness along a direction parallel to a tube axis of piezo tube 105that is sufficient to allow optical fiber to buckle when the distancebetween whirling distal joint 120 and buckling distal joint 125 isshortened. Optionally, buckling of optical fiber 110 may occur when thedistance between whirling distal joint 120 and buckling distal joint 125is decreased by more than a threshold amount. Example threshold amountsinclude 5 μm or less. Optionally, the axial stiffness may be equal to orgreater than a lateral stiffness along one or more lateral axesperpendicular to the tube axis of piezo tube 105.

FIG. 1 illustrates three different configurations of optical fiber 110to depict the advantage in deflection of optical fiber 110 that may beachieved through buckling. Optical fiber 110 is depicted in neutralorientation 130 in blue, where the optical fiber does not deflect. Piezotube 105 may be induced to undergo a whirling motion through suitableapplication of voltages at points along piezo tube 105. Whirling motionmay represent a circular, spiral, lissajou, or pseudo-circular motion ofan end of an object. Whirling of piezo tube 105 may induce a distal endof optical fiber 110 to also undergo a whirling motion, such thatoptical fiber 110 may obtain a maximum whirling deflection depicted bywhirling orientation 140 in green. It will be appreciated that whirlingorientation 140 may represent the maximum deflection of optical fiber110 that can be achieved by whirling alone. It will be furtherappreciated that the relative distances and sizes of objects andelements depicted in FIG. 1 are not to scale and are for illustrativepurposes only in order to more clearly depict the advantages achieved bythe instant inventions. Orientation 150 in red may represent the maximumdeflection of optical fiber 110 that can be achieved by a combination ofwhirling and buckling of optical fiber 110 between whirling distal joint120 and buckling distal joint 125.

It will be appreciated that buckling of optical fiber 110 may occur atany orientation of optical fiber 110 as it undergoes whirling motion. Itmay be advantageous for buckling of optical fiber 110 to take place whenoptical fiber is displaced through whirling of piezo tube 105 so thatthe direction of buckling is predictable and/or controllable. Forexample, when optical fiber 110 is in neutral orientation 130 andbuckling is induced by reducing a distance between whirling distal joint120 and buckling distal joint 125, the buckling may occur in anydirection, which may be unpredictable. By inducing buckling of opticalfiber 110 when optical fiber already is displaced through a whirlingmotion of piezo tube 105, such as in orientation 140, the direction ofbuckling may be predictable and relate to the whirling motion, such thatan increase in the deflection of optical fiber 110 may be achieved, asdepicted in orientation 150.

FIG. 2A provides a schematic illustration of a cross sectional view ofpiezo tube 200. As illustrated, piezo tube 200 includes piezo body 205,four electrodes 210, 215, 220, and 225 and a central opening 230.Electrodes 210-225 advantageously allow for application of voltages toenable deformation of piezo tube 200 in multiple directions. FIG. 2Bdepicts motion (exaggerated) of a distal end of the piezo tube 200 in acircular pattern, referenced to the neutral position 240, by applicationof appropriate voltages to the four electrodes 210-225. An innerelectrode 235, positioned in electrical contact with the inner surfaceof piezo tube 200, may be included, which may correspond to a platingpositioned on the internal surface of opening 230. Optionally, the innerelectrode may provide a voltage ground or other reference voltage fromwhich all other voltages are offset. Alternatively or additionally, oneor more additional electrodes may be positioned in electrical contactwith one or both ends of the piezo tube 200. Piezo tube 200 may be thesame as or different from other piezo tubes described herein, such aspiezo tube 105.

FIG. 4 provides a plot illustrating example piezo drive voltages forwhirling of a distal end of a piezo tube. For example, the depictedpiezo drive voltages may be applied to the four electrodes 210-225 toinduce whirling of a distal end of a piezo tube, and reflect a drivefrequency of about 25 kHz. Other frequencies may be useful for whirlingvoltages, including frequencies of between about 10 kHz and about 80kHz, such as between about 15 kHz and about 40 kHz or between about 40kHz and about 75 kHz. It will be appreciated that a magnitude oramplitude of the whirling voltages may change as a function of time inorder to increase or decrease a whirling deflection. For example, thewhirling voltages may exhibit a change in magnitude or amplitude fromabout 0 V, representing the neutral position or zero deflection, to amaximum magnitude or amplitude, representing maximum whirlingdeflection, to allow for a distal end of piezo tube 200 to follow aspiral-shaped deflection or whirling pattern. U.S. patent applicationSer. No. 14/156,366, filed on Jan. 15, 2014, and hereby incorporated byreference, describes additional details about piezo drive voltages andsuitable electronics to induce whirling of an optical fiber.

FIG. 3 provides a schematic illustration of an example fiber scanningsystem 300, which may be the same as or different from fiber scanningsystem 100 depicted in FIG. 1. Fiber scanning system 300 includes piezotube 305, optical fiber 310 passing through piezo tube 305, support tube315 mechanically coupled to piezo tube 305, and buckling piezo 320disposed inside support tube 315 and mechanically coupled to opticalfiber 310. As illustrated, piezo tube 305 has a distal tube end 325 anda proximal tube end 330; optical fiber 310 has a distal fiber end 335and a proximal fiber end 340; support tube 315 has a distal end 345 anda proximal end 350; buckling piezo 320 has a distal piezo end 355 and aproximal piezo end 360.

As illustrated, optical fiber 310 and distal tube end 325 of piezo tube305 are mechanically coupled at distal whirling joint 365; proximal tubeend 330 of piezo tube 305 and distal end 345 of support tube 315 aremechanically coupled at proximal whirling joint 370; optical fiber 310and distal piezo end 355 of buckling piezo 320 are mechanically coupledat buckling distal joint 375; proximal piezo end 360 of buckling piezo320 and proximal end 350 of support tube 315 are mechanically coupled atbuckling proximal joint 380.

As illustrated, distal tube end 325 of piezo tube 305 is positionedbetween distal fiber end 335 of optical fiber 310 and proximal tube end330 of piezo tube 305; proximal tube end 330 of piezo tube 305 ispositioned between proximal fiber end 340 of optical fiber 310 anddistal tube end 325; distal piezo end 355 of buckling piezo 320 ispositioned between proximal tube end 330 of piezo tube 305 and proximalpiezo end 360 of buckling piezo 320.

When buckling of optical fiber 310 is induced, for example by decreasingthe distance between distal whirling joint 365 and distal buckling joint375, optical fiber 310 buckles in buckling zone 385 (i.e., betweendistal whirling joint 365 and distal buckling joint 375). An innerdiameter of piezo tube 305 may be of a sufficient diameter toaccommodate buckling of optical fiber 310 in buckling zone 385 withoutoptical fiber 310 contacting the inner surface of piezo tube 305.

A structural loop may be used to describe the conceptual flow of forcesin fiber scanning system 300. It will be appreciated that structuralloops may be useful in determining system stiffness, symmetry, dynamicresponse, etc. It will further be appreciated that the flow of forcethrough buckling zone 385 is used to induce buckling of optical fiber ina lateral motion. The lateral motion may amplify displacement of distalfiber end 335 relative to the unbuckled configuration. The lateralmotion may arise due to movement of distal buckling joint 375 along thedisplacement direction, which is in an axial direction (verticaldirection in FIG. 3). In FIG. 3, starting from the bottom of the figureat proximal buckling joint 380, forces for the structural loop flow upbuckling piezo 320 to distal buckling joint 375, from distal bucklingjoint 375 radially into optical fiber 310, upward along optical fiber310 to distal whirling joint 365, from distal whirling joint 365radially into piezo tube 305, downward along piezo tube 305 to proximalwhirling joint 370, from proximal whirling joint 370 radially to supporttube 315, downward along support tube 315 to proximal buckling joint380, and from proximal buckling joint 380 radially back to bucklingpiezo 320. It will be appreciated that the unconstrained portion ofoptical fiber 310 between distal whirling joint 365 and distal fiber end335 falls outside the structural loop, indicating that this portion ofoptical fiber 310 is substantially free from forces in the structuralloop. However, it will be appreciated that buckling of the optical fiber310 in buckling zone 385 may impact the orientation of optical fiber 310at distal whirling joint 365. This may allow for a deflection of thedistal fiber end 335 to be achieved by buckling of optical fiber 310 inbuckling zone 385.

Voltages may be applied to buckling piezo 320 at or proximal to distalpiezo end 355 and at or proximal to proximal piezo end 360 in order toinduce a buckling displacement. Depending on the configuration,application of voltages to buckling piezo 320 may cause buckling piezo320 to expand or contract along a piezo axis, such as in the verticaldirection in FIG. 3. As illustrated in FIG. 3, expansion of bucklingpiezo 320 along the piezo axis will result in a displacement of distalbuckling joint 375 such that a distance between distal buckling joint375 and distal whirling joint 365 is decreased to induce buckling ofoptical fiber 310 in buckling zone 385.

FIG. 5 provides a plot illustrating example buckling drive voltages fordriving a buckling piezo to induce increased buckling of an opticalfiber as a function of time. The repetition rate of the sawtooth voltageprofile shown in FIG. 5 is about 50 Hz, which may represent a frame rateor refresh rate of a display for a fiber scanning display incorporatinga fiber scanning system. It will be appreciated that other bucklingdrive voltages and configurations may be used. For example, otherrepetition frequencies may be used, such as frequencies between about 15Hz and about 300 Hz, including common frame rates or refresh rates ofabout 23.976 Hz, about 24 Hz, about 25 Hz, about 29.97 Hz, about 50 Hz,about 59.94 Hz, about 60 Hz, about 85 Hz, about 120 Hz, and about 240Hz. Other voltage profiles may be used, such as triangular profiles,sinusoidal profiles, trapezoidal profiles, square profiles, etc.Additionally, buckling drive voltage profiles may include periods ofzero voltage, such as at the beginning of a cycle, which may represent adelay before the start of buckling of an optical fiber. Inclusion of adelay may be useful, for example, to allow for a whirling voltage tofirst generate a deflection of a suitable magnitude in the optical fiberbefore application of a buckling motion is introduced. In this way, thedirection of buckling may be controlled to match the direction of thedeflection instead of inducing random buckling which may occur at low orzero initial whirling displacements.

It will be appreciated that buckling piezos used in fiber scanningsystems described herein may take on any suitable configuration and mayinclude one or more electrodes, such as positioned at opposite ends ofthe buckling piezos. As illustrated in FIG. 3, buckling piezo 320 isconfigured as a tubular piezo. Use of a tubular piezo for buckling piezomay be advantageous and provide a cylindrically symmetric configuration.Other embodiments are contemplated, such as where buckling piezocomprises one or more separate, non-tubular, piezos. Optionally,buckling piezo may incorporate or otherwise comprise a piezo stack,corresponding to a plurality of individual piezo elements stackedtogether. It will be appreciated that piezos, including tubular piezos,piezo stacks, etc., may be commercially available. Optionally, a piezostack may refer to a construction of a plurality of individualpiezoelectric material layers that are electrically connected inparallel such that a single voltage may be simultaneously applied to oracross each of the individual piezoelectric material layers. Use ofpiezo stacks may be advantageous, in some embodiments, as a piezo stackmay exhibit a larger overall displacement for a particular voltage thana similarly sized single piezo element.

FIG. 6 provides a schematic illustration of an example fiber scanningsystem 600 including a buckling piezo comprising a piezo stack. Fiberscanning system 600 depicted in FIG. 6 is similar to fiber scanningsystem 300 depicted in FIG. 3. For example, fiber scanning system 600includes piezo tube 605, optical fiber 610 passing through piezo tube605, support tube 615 mechanically coupled to piezo tube 605, andbuckling piezo stack 620 disposed inside support tube 615 andmechanically coupled to optical fiber 610. As illustrated, piezo tube605 has a distal tube end 625 and a proximal tube end 630; optical fiber610 has a distal fiber end 635 and a proximal fiber end 640; supporttube 615 has a distal end 645 and a proximal end 650; buckling piezostack 620 has a distal piezo end 655 and a proximal piezo end 660. Itwill be appreciated that, while buckling piezo stack 620 is illustratedas having five individual piezo components, more or fewer individualpiezo components may be included in a piezo stack.

As illustrated, optical fiber 610 and distal tube end 625 of piezo tube605 are mechanically coupled at distal whirling joint 665; proximal tubeend 630 of piezo tube 605 and distal end 645 of support tube 615 aremechanically coupled at whirling proximal joint 670; optical fiber 610and distal piezo end 655 of buckling piezo stack 620 are mechanicallycoupled at distal buckling joint 675; proximal piezo end 660 of bucklingpiezo stack 620 and proximal end 650 of support tube 615 aremechanically coupled at buckling proximal joint 680. Buckling of opticalfiber 610 occurs in buckling zone 685, which is positioned betweendistal whirling joint 665 and distal buckling joint 675.

In operation, one or more voltages may be provided to piezo tube 605 toinduce motion of distal tube end 625 of piezo tube 605, such as by wayof one or more electrodes of piezo tube 605. Similarly, one or morevoltages may be provided to buckling piezo stack 620 to induce axialexpansion and/or contraction of buckling piezo stack 620 along the tubeaxis of buckling piezo stack, such as by way of one or more electrodesof buckling piezo stack 620. One or more voltage sources may bepositioned in electrical communication or electrical contact with theelectrodes of piezo tube 605 and piezo stack 620. As described abovewith reference to FIGS. 4 and 5, whirling voltages having a frequency ofbetween about 10 kHz and about 80 kHz may be applied to piezo tube 605to induce whirling of distal tube end 625 of piezo tube 605 and opticalfiber 610, such as at positions between distal whirling joint 665 anddistal fiber end 635, by the one or more voltage sources. Bucklingvoltages having a repetition frequency of between about 15 Hz and about300 Hz may be applied to buckling piezo stack 620 to induce expansionand/or contraction of buckling piezo stack 620 by the one or morevoltage sources.

In the configurations described in FIGS. 3 and 6, the buckling of theoptical fiber is achieved by expanding the buckling piezo or bucklingpiezo stack. Configurations are contemplated, however, where buckling isachieved by contracting a piezo. For example, in another configuration,a distal buckling joint may be mechanically attached to proximalwhirling joint and, instead of the optical fiber being mechanicallycoupled to the buckling piezo or buckling piezo stack at the distalbuckling joint, the optical fiber may be mechanically coupled to thebuckling piezo or piezo stack at a proximal buckling joint such that thebuckling zone is expanded to the region between the distal whirlingjoint and the proximal buckling joint. To induce buckling of the opticalfiber in this alternative configuration, a contraction of the bucklingpiezo or buckling piezo stack along the piezo axis will result in adisplacement of the proximal buckling joint such that a distance betweenthe proximal buckling joint and the distal whirling joint is decreased.Such a configuration may provide a number of advantages includingoptional elimination of the support tube, due to the mechanical couplingof the piezo tube and the buckling piezo or buckling piezo stack.

Additional fiber scanning system configurations are further contemplatedherein where a single piezo tube is used for both whirling and buckling.For example, FIG. 7 provides a schematic illustration of a fiberscanning system 700 using a single piezo tube for buckling and whirlingof an optical fiber. Fiber scanning system 700 includes piezo tube 705and optical fiber 710 passing through piezo tube 705. Piezo tube 705 hasa distal tube end 715 and a proximal tube end 720 and optical fiber 710has a distal fiber end 725 and a proximal fiber end 730. Distal tube end715 of piezo tube 705 is positioned between distal fiber end 725 ofoptical fiber 710 and proximal tube end 720 of piezo tube 705. Proximaltube end 720 is positioned between proximal fiber end 730 of opticalfiber 710 and distal tube end 715 of piezo tube 705.

Fiber scanning system also includes distal joint 735, which mechanicallycouples the distal tube end 715 of piezo tube 705 and optical fiber 710,and proximal joint 740, which mechanically couples the proximal tube end720 of piezo tube 705 and optical fiber 710. Advantageously, distaljoint 735 and proximal joint 740 exhibit mechanical characteristics forfacilitating buckling of optical fiber 710 in buckling zone 745 betweendistal joint 735 and proximal joint 740. For example, distal joint 735may exhibit an axial stiffness along an axis of piezo tube 705 that isof a sufficient magnitude to permit buckling of optical fiber 710 byshortening a length of piezo tube 705 between distal joint 735 andproximal joint 740. Distal joint 735 may exhibit a lateral stiffnessalong one or more lateral directions perpendicular to the tube axis ofpiezo tube 705 that is of a sufficient magnitude to accommodate lateralor angular deflections of optical fiber such that buckling of opticalfiber between distal joint 735 and proximal joint 740 causesdisplacement of the distal fiber end 725 of optical fiber 710.Optionally, the axial stiffness of distal joint 735 may be less than orabout equal to a lateral stiffness of distal joint 735. Additionally oralternatively, proximal joint 740 may exhibit an axial stiffness alongan axis of piezo tube 705 that is of a sufficient magnitude to permitbuckling of optical fiber 710 by shortening a length of piezo tube 705between distal joint 735 and proximal joint 740. In some embodiments, noconstraints are imposed on the lateral or axial stiffness of proximaljoint 740. Optionally, a lateral stiffness of proximal joint 740 is of amagnitude sufficient to provide a fixed and non-rotatable joint suchthat angular deflection of optical fiber 710 at proximal joint 740 isprevented.

To achieve the desired whirling and buckling motions of piezo tube 705,voltages may be applied to piezo tube 705 with different frequencycharacteristics. As described above and with reference to FIGS. 4 and 5and their associated description, the whirling voltages may have ahigher frequency than the buckling voltage. The buckling and whirlingvoltages may be applied to piezo tube 705 as a superposition of thebuckling voltage and a whirling voltage. In this way, an overall lengthof piezo tube 705 may be controlled by way of a common buckling profilecomponent of the voltages applied to each of, for example, fourelectrodes of piezo tube 705, while the whirling motion of piezo tube705 may be controlled by way of the individual whirling voltagecomponents of each of the voltages applied to the four electrodes.

FIGS. 8A-8C provide schematic views of a hub-and-frame based whirlingmechanism that is useful with the disclosed optical fiber scanningsystems. FIG. 8A shows a perspective view of a first side of an opticalscanning system 800. Optical scanning system 800 includes tapered fiber805. Light emitted from a distal end 810 of tapered fiber 805 isprojected. The optical scanning system 800 also includes a frame 815 andhub 820 driven by piezoelectric elements 825 (not visible in FIG. 8A).Piezoelectric elements 825 are coupled to both frame 815 and hub 820 tocooperatively induce oscillation of tapered fiber 805 in a predefinedpattern.

FIG. 8A illustrates a gap 830 between hub 820 and frame 815. In someembodiments, hub 820 can be configured to rotate or tilt in place toachieve a desired scan pattern of tapered fiber 805 and in otherembodiments, hub 820 can be configured to shift laterally to induce thedesired scan pattern. While hub 820 is depicted having a circular shapeit should be appreciated that many other shapes such as elliptical,rectangular and other polygonal geometries are also possible.

FIG. 8B shows how hub 820 can be coupled to frame 815 by multipleflexures 835. Flexures 835 can have a strain sensor incorporated withinframe 815 and/or flexure 835. Actuation of piezoelectric elements 825extends and contracts longitudinally to maneuver hub in a pattern thatmaneuvers distal end 810 of tapered fiber 805 in a circular pattern, forexample. This movement can be accomplished by sequentially actuatingpiezoelectric elements 825. For example, a first piezoelectric elementcan be actuated first, followed by a second piezoelectric element,located adjacent clockwise or counterclockwise from first piezoelectricelement, followed by a third piezoelectric element and a fourthpiezoelectric element. Actuation may follow the control signal as shownin FIG. 4, for example. Although four piezoelectric elements areillustrated, two or more piezoelectric elements (e.g., 2-20) may beused. When only two piezoelectric elements are used, for example, eachelement may be used to first expand in one direction to generate a firstlateral deflection and then contract to generate a second laterdeflection opposite to first lateral deflection. In some embodiments,piezoelectric element on opposing sides of hub 820 can be actuatedconcurrently, such as where one piezoelectric element extendslongitudinally and the other contracts longitudinally. In someembodiments, piezoelectric elements are on opposing sides of hub 820. Byvarying actuation of piezoelectric elements, varying scan patterns canbe achieved.

FIG. 8C shows a close up view of hub 820 and where piezoelectricelements 825 are attached to hub 820 by flexures 835. Strain sensors 840can be adjacent to or extending across flexures 835. Strain sensors 840can be configured to monitor movement of hub 820 and tapered fiber 805.Strain sensors 840 can be configured to monitor twisting and flexing offlexures 835. The twisting and flexing of flexures 835 monitored bystrain sensors 840 can be used to carry out closed loop feedback controlto achieve a consistent desired scan pattern. In some embodiments, eachflexure can include multiple strain sensors 840 to measure differenttypes of stresses being experienced by each of flexures 835. FIG. 8Dalso shows a close-up view of how piezoelectric elements 825 arearranged above and/or within channels 845 of frame 815. Channels 845 canbe arranged and shaped to accommodate lateral motion of piezoelectricstrips 825 during actuation and movement of hub 820.

FIG. 8D shows a side cross-sectional view of a hub-and-frame actuationbased whirling mechanism incorporated into a fiber scanning system withbuckling actuation. As illustrated, frame 815 is mechanically attachedto the distal end of buckling piezo 850. Buckling piezo 850 ismechanically attached to proximal end of buckling piezo 850 by way ofelement 855, which may correspond to a proximal buckling joint. Bycompressing the distance between element 855 and hub 820, tapered fiber805 can be induced to buckle along a lateral direction, as indicated byarrow 860 in FIG. 8D. Buckling actuation may follow the control signaldepicted in FIG. 5, for example, where buckling may ramp over time asdistal end 810 of tapered fiber 805 undergoes whirling, such as along aspiral pattern. Although FIG. 8D shows the piezo elements 825 aspositioned inside buckling piezo 850, embodiments may include where thepiezo elements 825 are on an opposite side of frame 815 and hub 820 andcloser to the tapered portion of fiber 805. Configurations are alsocontemplated where piezo elements 825 are positioned within gap 830.

It will be appreciated that, when used in a fiber scanning display, thewhirling voltage of a sinusoidal signal may have an amplitude thatincreases as a function of time, which may result in the distal end ofthe optical fiber being maximally deflected, such as along a spiralpattern, further and further from a zero position. The minimum tomaximum sinusoidal amplitude change may have a repetition rate matchinga refresh or frame rate of the display. The buckling voltage amplitudemay similarly increase as a function of time, with a repetition ratematching a refresh or frame rate of the display. These amplitudeincreases may optionally be synchronized. Optionally, the application ofthe buckling voltage may be delayed by a particular amount of time inorder for whirling of the optical fiber to begin so that the bucklingmay occur at a time where the buckling direction is predictable andmatches the whirling direction since, in some embodiments, at low orzero deflection the application of the buckling voltage may causebuckling to occur in an unpredictable direction. Additionally oralternatively, the application of the buckling voltage may be delayed bya particular amount of time until the additional deflection gains thatmay be achieved by buckling are needed, such as near the time when thewhirling deflection is close to, nearing, or otherwise reaching itsmaximum range.

Methods for scanning an optical fiber are also disclosed herein. In ageneral method, a first voltage is applied to an optical fiber scanningsystem to induce whirling of an optical fiber; a second is furtherapplied to the optical fiber scanning system to induce buckling of theoptical fiber. It will be appreciated that any of the optical fiberscanning systems described herein may be used with the disclosedmethods, such as any of the optical fiber scanning systems depicted inFIGS. 1, 3, 6, 7, and 8A-8D. For example, the first voltage may beapplied to a piezo tube and the second voltage may be applied to abuckling piezo. In another example, both the first and second voltagesare applied to a single piezo tube. Optionally, the first and secondvoltages are superimposed.

The first voltage may have a frequency representative of the motionassociated with whirling the optical fiber, and may correspond to one ormore sinusoidal voltage profiles, which may increase in amplitude inorder to whirl the optical fiber in a spiral pattern. The frequency ofthe first voltage may match or approximately match the natural resonantfrequency of the oscillating portion of the optical fiber. Depending onthe configuration, this frequency may fall within the range of about 10kHz to about 80 kHz. The first voltage may also exhibit a slowerrepetition frequency representative of a refresh or frame rate for adisplay, during which the high frequency whirling voltage is repeated towhirl the optical fiber in a repeated spiral motion.

The second voltage, associated with the buckling motion, may also have arepetition frequency representative of a refresh or frame rate for thedisplay. Depending on the configuration, this frequency may fall withinthe range of about 15 Hz to about 300 Hz, and repetition frequenciesmatching common refresh rates of 60 Hz or 120 Hz may be used. Asdescribed above, the second voltage may have a square, sawtooth,triangular, trapezoidal or other profile. Optionally, the second voltagemay increase in amplitude during each repetition and may also includeone or more periods of constant or decreasing voltage. Optionally, anincrease in the second voltage amplitude may be synchronized with all orpart of an increase in amplitude of the first voltage.

It will be appreciated that more or fewer components may be included inthe fiber scanning systems described herein. For example, fiber scanningsystems may include one or more voltage sources in electricalcommunication or electrical contact with a piezo, such as a piezo tubeand/or a buckling piezo or piezo stack. Voltage sources useful with thesystems and methods described herein include computer controlled voltagesources, programmable voltage sources, etc. Voltages applied to piezomaterials may take on any suitable magnitude. For example, low voltagepiezo materials may be used with the methods and systems describedherein, which may be driven by application of voltages having magnitudesbetween about 0 V and about 150 V. Optionally, higher or lower maximumvoltage piezos may be employed. It will be appreciated that, in someembodiments, a computer may generate a control voltage, such as avoltage between about 0 V and about 10 V or between about −10 V andabout 10 V, for example, and this control voltage may be used to drive aprogrammable voltage source, such as a voltage drive or amplifier, as aninput signal to the programmable voltage source. The programmablevoltage source may then convert and/or amplify the input signal to ahigher voltage signal, such as between about 0 V and about 100 V orbetween about −100 V and about 100 V, for example, to drive a piezo orpiezo stack.

Optionally, optical sources may be used with the systems and methodsdescribed herein. For example, fiber scanning systems may include one ormore optical sources optically coupled to an optical fiber to permitelectromagnetic radiation to be waveguided and or otherwise passedthrough the optical fiber to generate an electromagnetic radiationoutput at a distal fiber end of an optical fiber. Such a configurationmay correspond, at least in part, to a fiber scanning display. Opticalsources may be switchable, computer controlled, and/or programmable. Bysynchronously controlling the timing of outputs generated by an opticalsource as the distal fiber end of the optical fiber is moved by whirlingand/or buckling, optical images may be output. It will be appreciatedthat a variety of optical sources are useful with the systems andmethods disclosed herein including, but are not limited to, laseroptical sources, light emitting diodes, etc. Optical sources may includemultiple wavelength sources or single wavelength sources. Use ofmultiple wavelength sources may be useful for generation of full colorimages.

Optionally, fiber scanning systems may include one or more opticalcomponents to facilitate optical coupling of an optical source to anoptical fiber, such as lenses, prisms, filters, etc. Optionally, one ormore optical components may be optically coupled to the optical fiber tofacilitate outputting an image by the fiber scanning system, such as alens, filter, or other element, optionally positioned in opticalcommunication with a distal fiber end of the optical fiber.

The invention may be further understood by reference to the followingnon-limiting example.

Fiber Scanning System with Buckling Piezo Actuator

An optical fiber scanning system, similar to that shown in FIG. 7, wasconstructed as follows. An optical fiber of about 125 μm diameter wasinserted into a 4-electrode radially poled piezo tube. The optical fiberhad a cantilever length between the distal end of the piezo tube and thedistal end of the optical fiber of about 2.5 mm. The optical fiber wasfixed to a proximal buckling joint on a proximal end of the piezo tube.The piezo tube had a length of about 2.4 mm from the distal end to theproximal buckling position. Sinusoidal voltages of increasing amplitudewere applied to each of the electrodes, phase shifted by 90 degrees toinduce an oscillatory whirling motion. Triangular voltages were appliedto all electrodes as an offset to each of the sinusoidal voltages toinduce a change in the overall length of the piezo tube for bucklingmotion. Photographs of the constructed optical fiber scanner system areprovided in FIG. 9, showing (clockwise from top) an overhead view, anupper side view, a middle side view, a lower side view, and an alternatelower side view.

The terms and expressions which have been employed are used as terms ofdescription and not of limitation, and there is no intention in the useof such terms and expressions of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed. Thus, it should be understood that although thepresent invention has been specifically disclosed by preferredembodiments and optional features, modification and variation of theconcepts herein disclosed may be resorted to by those skilled in theart, and that such modifications and variations are considered to bewithin the scope of this invention as defined by the appended claims.

The above description of exemplary embodiments of the invention has beenpresented for the purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdescribed, and many modifications and variations are possible in lightof the teaching above. The embodiments were chosen and described inorder to explain the principles of the invention and its practicalapplications to thereby enable others skilled in the art to utilize theinvention in various embodiments and with various modifications as aresuited to the particular use contemplated.

When a group of substituents is disclosed herein, it is understood thatall individual members of those groups and all subgroups and classesthat can be formed using the substituents are disclosed separately. Whena Markush group or other grouping is used herein, all individual membersof the group and all combinations and subcombinations possible of thegroup are intended to be individually included in the disclosure. Asused herein, “and/or” means that one, all, or any combination of itemsin a list separated by “and/or” are included in the list; for example“1, 2 and/or 3” is equivalent to “1 alone, 2 alone, 3 alone, both 1 and2, both 1 and 3, both 2 and 3, or all of 1, 2 and 3”.

Every formulation or combination of components described or exemplifiedcan be used to practice the invention, unless otherwise stated. Specificnames of materials are intended to be exemplary, as it is known that oneof ordinary skill in the art can name the same material differently. Oneof ordinary skill in the art will appreciate that methods, deviceelements, and starting materials, other than those specificallyexemplified can be employed in the practice of the invention withoutresort to undue experimentation. All art-known functional equivalents,of any such methods, device elements, and starting materials, areintended to be included in this invention. Whenever a range is given inthe specification, for example, a temperature range, a time range, afrequency range, or a composition range, all intermediate ranges andsubranges, as well as all individual values included in the ranges givenare intended to be included in the disclosure. All or portions ofdifferent embodiments described herein may be combined in any suitablemanner without departing from the spirit and scope of the invention.However, other embodiments of the invention may be directed to specificembodiments relating to each individual aspect, or specific combinationsof these individual aspects.

What is claimed is:
 1. A system comprising: an optical fiber having adistal fiber end and a proximal fiber end; a first electromechanicaltransducer mechanically coupled to the optical fiber between the distalfiber end and the proximal fiber end, wherein the firstelectromechanical transducer is configured to apply a buckling force tothe optical fiber by reducing a length of the first electromechanicaltransducer between a distal buckling end of the first electromechanicaltransducer and a proximal buckling end of the first electromechanicaltransducer; and a second electromechanical transducer mechanicallycoupled to the optical fiber between the distal fiber end and theproximal fiber end, wherein the second electromechanical transducer isconfigured to excite whirling of the distal fiber end.
 2. The system ofclaim 1, wherein the distal fiber end is unconstrained.
 3. The system ofclaim 1, wherein the buckling force periodically ramps in amplitude,wherein a whirling amplitude for whirling of the optical fiberperiodically ramps, and wherein ramping of the buckling force andramping of the whirling amplitude are synchronized.
 4. The system ofclaim 1, wherein a first joint mechanically coupling the firstelectromechanical transducer and the optical fiber has a first axialstiffness along an axis parallel to a longitudinal axis of the opticalfiber, wherein a second joint mechanically coupling the secondelectromechanical transducer and the optical fiber has a second axialstiffness along the axis parallel to the longitudinal axis of theoptical fiber, and wherein the first axial stiffness and the secondaxial stiffness are sufficient to induce buckling of the optical fiberwhen a distance between the first joint and the second joint is reducedby a distance between 0.1 μm and 5 μm.
 5. The system of claim 1, whereinthe first electromechanical transducer corresponds to a buckling piezohaving the distal buckling end and the proximal buckling end, andwherein the optical fiber is mechanically coupled to the distal bucklingend, the proximal buckling end, or both the distal buckling end and theproximal buckling end.
 6. The system of claim 5, wherein the bucklingpiezo is a piezo tube or piezo stack and wherein the optical fiberpasses through the piezo tube or the piezo stack.
 7. The system of claim5, wherein the buckling piezo includes a plurality of electrodes forcontrolling a length of the buckling piezo by application of one or morevoltages.
 8. The system of claim 5, wherein the buckling force isapplied to the optical fiber by reducing a length of the buckling piezobetween the distal buckling end and the proximal buckling end.
 9. Thesystem of claim 1, wherein the second electromechanical transducercorresponds to a whirling piezo tube having a distal tube end and aproximal tube end, wherein the optical fiber passes through the whirlingpiezo tube, and wherein the distal tube end is mechanically coupled tothe optical fiber by a whirling distal joint.
 10. The system of claim 9,wherein the optical fiber is mechanically coupled to the distal tubeend, the proximal tube end, or both the distal tube end and the proximaltube end.
 11. The system of claim 9, wherein the whirling piezo tubeincludes a plurality of electrodes for controlling lateral deflectionsof the distal tube end by application of one or more voltages.
 12. Thesystem of claim 9, further comprising a support tube mechanicallycoupled to the whirling piezo tube and the first electromechanicaltransducer, wherein the first electromechanical transducer is positionedinside the support tube.
 13. The system of claim 9, wherein the distalfiber end extends beyond the distal tube end, and wherein the distaltube end is positioned between the distal fiber end and the proximaltube end.
 14. The system of claim 9, wherein the proximal fiber endextends beyond the proximal tube end, wherein the proximal tube end ispositioned between the proximal fiber end and the distal tube end, andwherein the optical fiber is not fixed to the proximal tube end.
 15. Thesystem of claim 9, wherein the whirling piezo tube has an inner diametersufficient to accommodate buckling of the optical fiber.
 16. The systemof claim 9, wherein the whirling distal joint has an axial stiffnessalong a longitudinal axis of the whirling piezo tube, wherein the axialstiffness is sufficient to induce buckling of the optical fiber, andwherein the whirling distal joint has a lateral stiffness that issufficient to accommodate lateral rotation of the optical fiber duringbuckling.
 17. The system of claim 9, wherein the first electromechanicaltransducer corresponds to a buckling piezo having the distal bucklingend and the proximal buckling end, wherein the distal buckling end ispositioned between the proximal tube end and the proximal buckling end,wherein the optical fiber and the distal buckling end are mechanicallycoupled by a buckling distal joint, and wherein movement of the bucklingdistal joint along a longitudinal fiber axis causes buckling of theoptical fiber between the buckling distal joint and the whirling distaljoint.
 18. The system of claim 17, further comprising a support tubemechanically coupled to the whirling piezo tube and the buckling piezo,wherein the buckling piezo is positioned inside the support tube,wherein the support tube has a distal end and a proximal end, whereinthe distal end of the support tube and the proximal tube end aremechanically coupled by a whirling proximal joint, and wherein theproximal end of the support tube and the proximal buckling end aremechanically coupled by a buckling proximal joint.
 19. The system ofclaim 1, wherein the second electromechanical transducer includes a hub,a frame surrounding the hub, and a plurality of lateralelectromechanical transducers mechanically coupled to the frame and tothe hub, wherein the optical fiber passes through the hub, and whereinthe hub is mechanically coupled to the optical fiber by a whirlingjoint.
 20. The system of claim 19, wherein the second electromechanicaltransducer further includes a plurality of flexures extending radiallyfrom the hub and coupling the hub to the frame.
 21. The system of claim19, wherein the lateral electromechanical transducers correspond topiezo elements including electrodes for controlling lateral deflectionsof the hub to excite whirling of the distal fiber end.
 22. The system ofclaim 1, wherein the first electromechanical transducer and the secondelectromechanical transducer comprise a piezo tube, wherein the piezotube has a distal tube end and a proximal tube end, wherein the opticalfiber passes through the piezo tube, and wherein the distal fiber endextends beyond the distal tube end, wherein the distal tube end and theoptical fiber are mechanically coupled at a distal joint, wherein theproximal tube end and the optical fiber are mechanically coupled at aproximal joint, wherein the distal joint and the proximal joint haveaxial stiffnesses along a longitudinal axis of the piezo tube that aresufficient to induce buckling of the optical fiber, wherein the distaljoint has a lateral stiffness that is sufficient to accommodate lateralrotation of the optical fiber during buckling, and wherein the piezotube has an inner diameter sufficient to accommodate buckling of theoptical fiber between the distal joint and the proximal joint.
 23. Thesystem of claim 22, wherein the distal tube end is positioned betweenthe distal fiber end and the proximal tube end, wherein the proximalfiber end extends beyond the proximal tube end, and wherein the proximaltube end is positioned between the proximal fiber end and the distaltube end.
 24. The system of claim 22, wherein the piezo tube includes aplurality of electrodes for controlling lateral deflections of thedistal tube end and for controlling a length of the piezo tube byapplication of one or more voltages.
 25. The system of claim 24, whereina buckling voltage simultaneously applied to the plurality of electrodescauses a length of the piezo tube along a longitudinal tube axis tochange, and wherein different whirling voltages applied individually tothe plurality of electrodes causes the distal tube end to deflectlaterally in a spiral configuration.
 26. A method comprising: applying afirst voltage to an optical fiber scanning system to induce whirling ofan optical fiber, wherein the optical fiber scanning system includes:the optical fiber, wherein the optical fiber has a distal fiber end anda proximal fiber end; a first electromechanical transducer mechanicallycoupled to the optical fiber between the distal fiber end and theproximal fiber end, wherein the first electromechanical transducer isconfigured to apply a buckling force to the optical fiber by reducing alength of the first electromechanical transducer between a distalbuckling end of the first electromechanical transducer and a proximalbuckling end of the first electromechanical transducer; and a secondelectromechanical transducer mechanically coupled to the optical fiberbetween the distal fiber end and the proximal fiber end, wherein thesecond electromechanical transducer is configured to excite whirling ofthe distal fiber end; and applying a second voltage to the optical fiberscanning system to induce buckling of the optical fiber.
 27. The methodof claim 26, wherein the first electromechanical transducer includes aplurality of electrodes, and wherein applying the second voltageincludes applying the second voltage to the plurality of electrodes toinduce longitudinal application of the buckling force.
 28. The method ofclaim 26, wherein the second electromechanical transducer includes aplurality of electrodes, and wherein applying the first voltage includesapplying the first voltage to the plurality of electrodes to inducelateral deflection of the optical fiber for exciting whirling of thedistal fiber end.
 29. The method of claim 26, wherein whirling of theoptical fiber causes the distal fiber end to deflect a firstpredetermined amount and wherein buckling of the optical fiber causesdeflection of the distal fiber end by a second predetermined amount thatis superimposed on the first predetermined amount.